Hard drives can fail at any time, this is why backup is important in the first place.
Does the drive at least spin up? can you hear it?
You can try to connect the drive to another computer just in case its a problem with your system.
You may also try another cable.
If the system is IDE chances are your CD/DVD drive is ide and you can connect it to that cable. It will be slower if the cable is a 40 wire only, but at least it will let you see it the cable is the issue.
The should give you a starting point, but no guarantee here, the drive may be dead.